Vertical transportation systems have numerous uses. Specifically, elevators are widely used for vertical transportation of people, materials, and other commodities. The applications of elevators include, but are not limited to, transportation in commercial and residential buildings, wind mills, mines, cruise ships, and also for material handling in shipyards, medical centers, and industrial facilities.
The prime requirements for elevators are safety and comfort. Conventional elevators use rail guides to provide vertical guidance and emergency safety stops. A set of drive cables from a traction motor are used to vertically move the elevator along the rail guides. Many safety systems have been developed for rail guides to enable mechanical locking in case of power breakdowns, or cable failure. However, rail guides increase the cost of installation, maintenance and severely compromise ride comfort.
FIGS. 1A-1B show a front view 100 and a side view 170 of a conventional elevator, respectively. The front view shows an elevator car 110 configured to move in a shaft along rail guides 150. Rollers 190 engage with the rail guides.
The car is hoisted in the shaft with hoist cables 120 wound around a hoist drum 130, which is driven by a traction motor 140. Compensator cables 125 are available with a compensator drum 160, which is not actuated. A counter weight 180 is provided on the rear side of the shaft.
As can be seen in FIG. 1, the cables in conventional elevators run parallel to the direction of up/down movement. This makes it difficult to provide lateral stability without the guide rails. In addition, as can be seen in a top view 171, the cables are generally attached to the top and bottom centers 175 of the car.
Typical elevator installation costs include shaft preparation and elevator component installation. A major cost involved in the process is for installing rail guides. Rail guides are available as short segments of steel that are bolted to a steel frame installed in the shaft of the elevator. At the joints of the rail guide segments, often, small (on the order of 1-2 cm) bumps are formed that hinder the ride quality, especially, resulting in large lateral accelerations, tilting and turning of the elevator. Such parasitic motions of the elevator result in poor ride comfort for the passengers. Precise alignment makes rail guides expensive to install, and further, alignment degrades over time causing lateral vibration, and increasing the associated maintenance costs.
Both first-time installation and post-installation rectification for degraded alignment are labor-intensive processes that require the whole elevator car and other cars in the shaft to be shut down for checking the rail guide alignments at each joint. In a twenty floor building, this may take months. Even after precise alignment, improving ride quality necessitates additional accessories such as one or more roller suspension assemblies and associated electronics and control systems to compensate challenges imposed by the rail guides.
In summary, rail guides pose installation, maintenance, and ride-quality challenges that severely undermine their cost-effectiveness.
Accordingly, there is a need to address disadvantages of rail guides in elevators.